In common practice Wade-Giles suffers from a fatal flaw. If the apostrophes are omitted from the system, Wade-Giles becomes "bastardized" (the correct term, even if sounds vaguely offensive) and largely useless. (Technically, Wade-Giles uses ayns, not apostrophes; but the distinction is not one most people need worry about.)
Here's a basic explanation of why the apostrophes matter so much. Wade-Giles uses apostrophes to distinguish between some related sounds.
Thus, with bastardized Wade-Giles, nothing written that contained any of the above sounds could be relied upon as correct, because without the apostrophes it is completely impossible to distinguish which of various sounds is meant.
For a real-world example, let's look at the way a Taipei MRT stop used to be romanized as "Kuting" (for 古亭). But because the apostrophes are routinely and erroneously omitted from Wade-Giles, it is completely impossible -- even for the relatively few people who are familiar with Wade-Giles -- to know if the name is really Ku-ting ("Guding" in Hanyu Pinyin and ㄍㄨ ㄉㄧㄥ in Zhuyin Fuhao), K'u-ting (Kuding, ㄎㄨ ㄉㄧㄥ), K'u-t'ing (Kuting, ㄎㄨ ㄊㄧㄥ), or Ku-t'ing (Guting, ㄍㄨ ㄊㄧㄥ). (Note that Hanyu Pinyin's Guting, has no such ambiguity and works well to show the correct pronunciation.)
That's four equally likely possibilities. If tones were included in the computations, there could be 64 different possible pronunciations of the two syllable "Kuting" -- hardly a useful representation of 古亭.
Unfortunately, this is not an isolated example. As it happens, 67 percent of Taipei street names have at least one of those sounds, and I don't doubt that the figure would be largely the same for other places in Taiwan and China. That means that even if all of the signs were spelled "correctly" and consistently in bastardized Wade-Giles, only one-third of them could be relied on as a reliable guide to pronunciation.
Using a system that can be relied upon only one-third of the time (and even then by very few people) makes no sense whatsoever -- but that's exactly what Taipei did for years before the city's move to Hanyu Pinyin.
It is no exagerration to say that before a couple of years ago the majority of Taiwan's street signs, place names, personal names, company names, and just about everything else written in a romanized form were wrong and led to much confusion. Taiwan's de facto "standard" of bastardized Wade-Giles has been a waste of time, money, and effort.
If you want to be understood when romanizing Chinese, use Hanyu Pinyin.